The invention relates to data processing systems and more particularly to an architectural arrangement for a SCSI disk controller integrated circuit (SDC IC) for transferring data between a disk memory and a SCSI bus of a data processing system.
Soon after the completion of the ANSI X3.131 standard for a small computer system interface (SCSI) various designs for SCSI disk controllers began to be implemented. The initial designs were implemented using off-the-shelf SSI, MSI, and LSI logic circuits. This approach led to SCSI disk controllers which were physically large and which could only be accommodated by large computer housings or disk memory housings. A good example of this is shown and discussed in the article "Single-board Controllers Manage More Than One Mass-storage Medium" appearing in ELECTRONIC DESIGN Vol 31, Issue No. 6 on pages 131 through 138. Having large computer/disk housings to accommodate a large printed circuit board with a large population of integrated circuits for a new SCSI disk controller was counter to the direction of the small computer industry, which is to make equipment smaller. Thus, to keep in step with the small computer industry with respect to physical size, a very large scale SCSI disk controller integrated circuit (SDC IC)is needed to replace most of the off-the-shelf SSI, MSI, and LSI circuits.
In addition to the physical size considerations, a SCSI disk controller which has numerous discrete logic circuits has high manufacturing costs over a SCSI disk controller which uses a SDC IC VLSI chip for many of the operations. Each electronic part takes time to locate and insert properly. Furthermore, each lead which is inserted has a probability of not making a proper electrical connection because of insertion/soldering errors. Such errors must be individually tested and corrected, which incurs the labor cost of a highly skilled technician. Thus, to reduce the manufacturing costs and the ultimate consumer expense, a SCSI disk controller using VLSI circuitry is needed to reduce the total part count.
It is an object of this invention to provide a SCSI disk controller which is not physically large relative to the small disk systems currently existing in the industry.
It is another object of this invention to provide an architectural arrangement for a SDC IC.
It is a further object of this invention to provide an architectural arrangement for a very large scale SDC IC for use, in conjunction with a small number of other electronic parts, to transfer data between a SCSI bus and a disk memory bus.